This invention relates to a fuel injection nozzle for injecting fuel into a combustion chamber of an internal combustion engine and, in particular, to a fuel injection nozzle suited to a diesel engine.
Generally, a diesel engine is louder in combustion noises, and poorer in combustion efficiency, than a gasoline engine. Various attempts have so far been made to eliminate drawbacks inherent in the diesel engine. It is known in the art that, in order to reduce the combustion noises in the diesel engine, fuel is injected by a fuel injection nozzle into a combustion chamber of the engine with a fuel injection rate decreased in an initial phase of a fuel injection period and increased in a final phase of the fuel injection period. For the fuel injection nozzle having such a fuel injection rate it is possible to reduce the combustion noises and suppress a sharp temperature rise within the combustion chamber and thus reduce an amount of NOx in an exhaust gas.
The fuel injection nozzle having the above-mentioned fuel injection rate is disclosed, for example, in Japanese Patent Disclosure (KOKAI) No. 151058/82. The known fuel injection nozzle has a nozzle needle for permitting a fuel injection hole to be opened and closed. In the initial phase of the fuel injection period the lift of the nozzle needle is restricted to a predetermined amount of lift through the abutment of the nozzle needle against the spring-urged adjustment piston. As a result, the cross-sectional area of the opening of the injection hole is small in the initial phase of the fuel injection period so that the fuel injection rate is suppressed to a smaller extent. Thereafter, the nozzle needle is further lifted against an urging force of the spring with the adjustment piston so abutted, resulting in an increase in the opening area of the injection hole and thus an increase in the fuel injection rate in a final phase of the fuel injection period.
In order to enhance the combustion efficiency of fuel in the combustion chamber it is necessary to enhance the atomization of fuel injection at an initial phase of the fuel injection period and thus to ignite the fuel in a better condition. However, no adequate consideration is paid to this aspect, failing to adequately enhance the engine output.